1. Field of the Invention
The present invention relates to data communication systems and, more particularly to identifying remote communication equipment and enhancing communication performance in data communications systems.
2. Description of the Related Art
Many communication standards have been adopted to ensure interoperability of communications systems built by different manufacturers that operate under the same protocol. Such standards define the sequence and type of signals that a particular communications system needs to follow in order to work properly with other communications systems implemented in accordance with the same standard.
In practice however different manufacturers build communications systems that deviate from the standards. Sometimes those deviations are intentional, e.g., to accommodate hardware limitations or to simplify software. Other times those deviations are unintentional and arise from hardware of software “bugs”. Once communication devices that differ from the standard are deployed in significant numbers it becomes important for other manufacturers of communications systems subsequently deployed to ensure interoperability with the already deployed deviating devices.
New communications equipment may compensate for deviations from the standard by already deployed devices when implementing a standard communication protocol. Unfortunately compensation for such deviations may also constitute a deviation from the standard and can break interoperability with other equipment implementing the same protocol. Furthermore, compensation for such deviation may require disabling one or more performance enhancing features of the protocol.
The International Telecommunication Union—Telecommunications Standardization Bureau (“ITU-T”) in Geneva, Switzerland, develops and publishes “Recommendations” that relate to communications protocols. The ITU-T Recommendations are non-binding international standards whose objective is to insure interoperability of communication equipment built by different vendors. For example, Recommendation V.90, which is incorporated herein by reference, is entitled A Digital Modem and Analogue Modem Pair for Use on the Public Switched Telephone Network (PSTN) at Data Signalling Rates of Up to 56 000 bit/s Downstream and Up to 33 600 bit/s Upstream, and describes one such protocol.
As part of the V.90 Recommendation the spectral characteristics of a signal emitted by a digital modem can be altered by a technique called “spectral shaping” which is described in paragraph 5.4.5 of the Recommendation. That technique allocates some of the data carrying capacity of the channel for the purpose of altering the spectrum of the signal to improve signal demodulation by the analog modem. The parameters of the “spectral shaping” are determined by the analog modem. One of those parameters is the number of bits used for spectral shaping per mapping frame (a group of six symbols). Spectral shaping improves as more bits are used but that reduces the data carrying capacity of the symbols. The analog modem determines the number of bits used by spectral shaping to optimise the throughput. In order to increase throughput, when the communication channel permits, the analog modem disables spectral shaping.
As an example of a failure of interoperability, it was determined during field testing that certain digital modems have a problem when spectral shaping is disabled. When an analog modem requests that spectral shaping be disabled, the particular digital modems function improperly and stop responding to any further communication. To insure interoperability with digital modems that deviate from the standard in that manner, an analog modem has to request spectral shaping even when line conditions do not require it. Since spectral shaping reduces data carrying capacity, the throughput is subsequently reduced. The V.90 Recommendation does not provide for the identification of the type or brand of the remote modem and thus spectral shaping has to always be enabled to ensure interoperability.
Accordingly, it would be desirable to be able to identify remote communication equipment in order to adjust communication performance according to device capability. More generally, it would be desirable to identify a remote communication device when the communication protocol under which it operates fail to provide a standard or convenient method to identify the remote device. It would be further desirable, based on that identification, to improve communication performance, compensate for deviations from communication standards or otherwise improve system capabilities.